Auto-invertible inverse polymer emulsion

ABSTRACT

The invention relates to an inverse polymer emulsion having the particular feature of auto-inverting without any need for the use of an inverting agent and containing a polymer of at least one water-soluble monomer and at least one LCST macromonomer. The invention also relates to the use of the inverse emulsion in the fields of the oil and gas industry, water treatment, slurry treatment, paper manufacturing, construction, mining, cosmetics, textiles, detergents or agriculture.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under section 371 ofInternational Application No. PCT/FR2019/052606 filed on Nov. 4, 2019,and published on May 14, 2020 as WO 2020/094960, which claims priorityto French Application No. 1860204, filed on Nov. 6, 2018. The entirecontents of WO 2020/094960 are hereby incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to the technical field of polymers as awater-in-oil emulsion, otherwise known as an inverse emulsion. Morespecifically, the invention relates to an inverse polymer emulsionhaving the particular feature of auto-inverting without requiring theuse of an inverting agent.

The invention also relates to the use of this inverse emulsion invarious fields such as the oil and gas, water treatment, slurrytreatment, paper manufacturing, construction, mining, cosmetics,textiles, detergents, and agriculture industries.

PRIOR STATE OF THE ART

Inverse polymer emulsions are widely used in various fields such aswater treatment, enhanced oil recovery and hydraulic fracturing.

The use of these inverse emulsions is based on dissolving the polymer inwater or brine. To that end, the inverse emulsion inverts so as torelease the polymer contained in the aqueous phase of the inverseemulsion. After release, the polymer is in the water or brine to whichthe inverse emulsion was added. To date, this inverse emulsion inversionstep involves the presence of inverting agents, which are generallyhydrophilic surfactants with a high HLB, generally greater than 10.

The presence of hydrophilic surfactants in an inverse polymer emulsionmay affect the viscosity and/or stability parameters of the inverseemulsion. This results in significant increases in the viscosity of theinverse emulsion (which can lead to caking) or by an acceleration of thephase separation (sedimentation of the polymer particles and occurrenceof an oily phase on the surface).

On the other hand, it is acknowledged that most hydrophilic surfactantsare ethoxylated products which may present environmental problems.

In addition, the hydrophilic surfactants must be selected specificallyaccording to the composition of the medium in which the inverse emulsionis implemented (water or brine), and according to the temperature ofthis medium, which requires a complex adjustment process for thehydrophilic surfactant to act as an inverting agent.

Thus, it would be advantageous to have an inverse emulsion which caninvert without using an inverting agent. Therefore, the problem whichthe present invention proposes to solve is to provide an inverseemulsion which auto-inverts without requiring the use of an invertingagent such as an oil-in-water surfactant.

DISCLOSURE OF THE INVENTION

The applicant surprisingly discovered that the introduction ofmacromonomer with lower critical solution temperature (LCST) in thepolymer during its synthesis in inverse emulsion could give the inverseemulsion an auto-inversion property.

This auto-inversion property means that the polymer dissolves in water(or brine) without necessarily resorting to the use of an invertingagent such as an oil-in-water surfactant. In addition, this emulsion canrapidly invert even under conditions of high temperature and/or highsalinity, which is of great interest, particularly in the fields of oiland gas recovery.

More specifically, the present invention relates to an auto-invertibleinverse emulsion comprising:

-   -   an oil,    -   some water,    -   at least one water-in-oil surfactant,    -   at least one polymer containing monomer units of at least one        water-soluble monomer and at least one LCST macromonomer.

The inverse emulsion according to the invention is advantageously freeof oil-in-water surfactant.

The present invention also relates to a polymeric aqueous solutionobtained by inversion of the inverse emulsion described above. Theinversion is advantageously carried out in the absence of anoil-in-water surfactant. It also relates to the use of the inverseemulsion described above to thicken an aqueous medium, or to flocculatesuspended particles or reduce the level of frictional resistance duringtransport of an aqueous medium.

Finally, the present invention also relates to the use of the inverseemulsion described above for the recovery of oil and gas, or for thetreatment of water, or for the treatment of slurry, or for themanufacture of paper, or in construction, or in the mining industry, orin the formulation of cosmetics, or in the formulation of detergents, orin the manufacture of textiles, or in agriculture.

Polymer

The polymer in the inverse emulsion is generally water-soluble orwater-swelling. The term “water-soluble polymer” is understood to mean apolymer which gives an aqueous solution when it is dissolved understirring at 25° C. and with a concentration of 50 g·L⁻¹ in water. Theterm “water-swelling polymer” is understood to mean a polymer whichswells and thickens an aqueous solution (water) in which it is placed at25° C.

The polymer is a polymer of at least one water-soluble monomer and atleast one LCST macromonomer. In other words, the polymer is obtainedfrom at least one water-soluble monomer and at least one LCSTmacromonomer. Therefore, it contains monomer units derived from themonomer(s) and macromonomer(s) mentioned. In other words, the polymer ofthe inverse emulsion according to the invention is a polymer of at leastone water-soluble monomer bearing at least one unsaturated function(advantageously, a vinyl group R1R2C═CR3-, R1, R2 and R3 beingindependently of one another a hydrogen atom or a hydrocarbon or anon-hydrocarbon group which may comprise heteroatoms) which might bepolymerized to form a backbone, and of at least one LCST macromonomer.Thus, the polymer comprises units derived from the water-soluble monomerand units derived from the LCST macromonomer.

As defined by IUPAC, a macromonomer is a polymer or oligomer bearing aterminal group that acts as a monomer, thus each polymer or oligomercorresponds to a monomer unit in the final polymer chain.

According to an advantageous embodiment, the molar percentage of units(monomer units) derived from LCST macromonomers in the polymer isbetween 10⁻⁵ and 5 mol % (≥10⁻⁵ mol % and ≤5 mol %) relative to thetotal number of moles of monomer units of water-soluble monomer(s) andLCST macromonomer(s), preferably between 10⁻⁴ and 1 mol %. Thispercentage is preferably greater than 10⁻³ mol % (≥10⁻³ mol %), evenmore preferably greater than 5.10⁻³ mol %. This percentage is preferablyless than 1 mol % relative to the total number of moles of monomer unitsof water-soluble monomer(s) and LCST macromonomer(s), preferably lessthan 0.1 mol %, preferably less than 8.10⁻² mol %, more preferably lessthan 6.10⁻² mol %, even more preferably less than 5.10⁻² mol %, evenmore preferably less than 4.10⁻² mol %.

In general, the amount of monomer units of a monomer (monomer ormacromonomer) corresponds to the amount of this monomer used in thepreparation of the polymer. This definition is applicable for thepreparation of the water-soluble copolymer or the macromonomer and,therefore, of the oligomer (see below).

According to an embodiment of the invention, the polymer may be obtainedby polymerizing at least one water-soluble monomer bearing at least oneunsaturated function and at least one LCST macromonomer. In other words,the water-soluble monomer(s) and the LCST macromonomers are polymerizedat the same time in a reactor. The polymer chain is formed gradually inthe presence of water-soluble monomers and LCST macromonomers.

According to another embodiment, a water-soluble prepolymer, called abackbone, is first obtained by polymerizing the water-soluble monomers,then, in a second step, the LCST oligomers are grafted onto saidprepolymer. A person skilled in the art is familiar with the techniquesfor grafting LCST macromonomers onto a polymer. Mention may be made, forexample, of patent application WO 2014/047243 which discloses thistechnique.

According to a third embodiment, the polymer may be obtained bypolymerizing water-soluble monomers on a structured LCST macromonomerobtained by controlled radical polymerization (RAFT) in the presence ofLCST monomers and at least one crosslinking agent. Therefore, thepolymers thus obtained are in a star-shaped form with an LCST core. Thecrosslinking agent may, in particular, be selected from the groupcomprising polyethylene unsaturated monomers (having at least two C═Cunsaturated functions), such as, for example, vinyl, allylic and acrylicfunctions and mention may be made, for example, of methylene bisacrylamide (MBA).

The polymer may also be obtained by the same technique but without usinga crosslinking agent for obtaining the macromonomer by controlledradical polymerization (RAFT).

Of course, methods other than these two methods for obtaining thepolymer may be used without departing from the scope of the invention.

The water-soluble monomers which may be used are preferably selectedfrom nonionic monomers, anionic monomers, cationic monomers andzwitterionic monomers. Preferably, they are selected from nonionic,anionic and cationic monomers.

The water-soluble monomer may be a nonionic monomer which may, inparticular, be selected from the group comprising vinyl monomers solublein water, and particularly acrylamide; methacrylamide; N-vinylformamide;and N-vinylpyrrolidone. Advantageously, at least one water-solublemonomer is acrylamide.

At least one water-soluble monomer may also be an anionic monomer. Theanionic monomer(s) which may be used in the context of the invention maybe selected from a large group. These monomers may have at least onefunction among the vinyl functions (for example, acrylic, maleic,fumaric, itaconic, allylic) or a malonic function, and they may containat least one group from carboxylate, phosphonate, phosphate, sulfate,sulfonate groups, or another anionically charged group. The anionicmonomer may be in acid form or else in the form of an alkaline earthmetal or an alkali metal or ammonium (in particular, quaternaryammonium) salt. Examples of anionic monomers are acrylic acid;methacrylic acid; itaconic acid; crotonic acid; maleic acid; fumaricacid; monomers of strong acid type exhibiting, for example, a functionof sulfonic acid or phosphonic acid type, such as 2-acrylamido2-methylpropanesulfonic acid, vinylsulfonic acid, vinylphosphonic acid,allylsulfonic acid, allylphosphonic acid, styrene sulfonic acid; and thewater-soluble salts of these monomers such as their alkali metal,alkaline earth metal, or ammonium (especially quaternary ammonium)salts.

At least one water-soluble monomer may optionally be a cationic monomerof vinyl type (for example, acrylamide, acrylic, allylic or maleic)having at least one ammonium function (for example, a quaternaryammonium). Mention may be made, in particular and without limitation, ofquaternized or salified dimethylaminoethyl acrylate (ADAME); quaternizedor salified dimethylaminoethyl methacrylate (MADAME);dimethyldiallylammonium chloride (DADMAC); acrylamido propyltrimethylammonium chloride (APTAC); and methacrylamido propyltrimethyl ammoniumchloride (MAPTAC).

Monomers of hydrophobic nature may also be used as a comonomer for thepreparation of the polymer, but at a concentration by weight based onthe total monomer content of preferably less than 5%. They arepreferably selected from the group comprising esters of (meth)acrylicacid having an alkyl, arylalkyl or ethoxylated chain; (meth)acrylamidederivatives having an alkyl, arylalkyl or dialkyl chain; cationicallylic derivatives; anionic or cationic hydrophobic (meth)acryloylderivatives; and derivatives of anionic or cationic monomers of(meth)acrylamide carrying a hydrophobic chain. The alkyl chains areadvantageously C8-C16. Most preferred is bromoalkylated C8-C16methacrylamide.

It is also possible to use a branching agent or a crosslinking agent.Such an agent is, for example, selected from methylene-bis-acrylamide(MBA), ethylene glycol diacrylate, tetraallyl ammonium polyethyleneglycol chloride, diacrylamide, cyanomethyl acrylate, epoxies andmixtures thereof.

It is also possible to use a free radical chain transfer agent, alsoknown as a chain stopper. The use of a chain transfer agent isparticularly advantageous for controlling the molecular weight of thepolymer obtained. By way of example of a transfer agent, mention may bemade of methanol, isopropanol, sodium hypophosphite, 2-mercaptoethanol,sodium methallylsulphonate, and mixtures thereof. A person skilled inthe art will adjust in a known manner the amounts of branching agent,and optionally of transfer agent or branching agent.

The polymer may be obtained by radical polymerization in inverseemulsion.

Polymerization techniques such as controlled radical polymerizationknown as RAFT (Reversible-Addition Fragmentation chain Transfer), NMP(Nitroxide Mediated Polymerization) or ATRP (Atom Transfer RadicalPolymerization), may be used to obtain the polymer.

According to the invention, the polymer has a molecular weightadvantageously of at least 0.5 million g/mol, preferably between 0.5 and40 million g/mol, more preferably between 5 and 30 million g/mol.Molecular weight is referred to as weight average molecular weight.

Molecular weight is determined by the intrinsic viscosity of thepolymer. The intrinsic viscosity may be measured by methods known to aperson skilled in the art and may be calculated from the values ofreduced viscosity for different polymer concentrations by a graphicmethod consisting in recording the values of reduced viscosity (y-axis)on the concentration (x-axis) and extrapolating the curve to zeroconcentration. The intrinsic viscosity value is recorded on the y-axisor using the least squares method. The molecular weight may then bedetermined by the Mark-Houwink equation:[η]=K M ^(α)[η] represents the intrinsic viscosity of the polymer determined by thesolution viscosity measurement method,

K represents an empirical constant (K=3.73.10⁻⁴),

M represents the molecular weight of the polymer,

α represents the Mark-Houwink coefficient (α=+0.66),

K and α depend on the particular polymer-solvent system.

LCST Macromonomer and its Synthesis

According to the general knowledge of a person skilled in the art, theLCST groups correspond to groups whose solubility in water for adetermined concentration is modified beyond a certain temperature andbased on the salinity. These are groups exhibiting a transitiontemperature by heating that defines their lack of affinity with thesolvent medium. Lack of solvent affinity results in clouding or loss oftransparency.

The minimum transition temperature is called “LCST” (Lower CriticalSolution Temperature). For each LCST group concentration, a transitiontemperature by heating is observed. It is greater than the LCST which isthe minimum point of the curve. Below this temperature, the polymer issoluble in water, above this temperature, the polymer loses itssolubility in water.

The LCST may be measured visually in the usual manner: the temperatureis determined when the cloud point appears, which is when the lack ofaffinity with the solvent occurs. The cloud point corresponds to theclouding or loss of transparency of the solution.

The LCST may also be determined according to the type of phasetransition, for example by DSC (Differential Scanning calorimetry), by atransmittance measurement or by a viscosity measurement.

Preferably, the LCST is determined by determining the cloud point bytransmittance according to the following protocol.

The transition temperature is measured for an LCST compound for asolution having a mass concentration of 1% by weight of said compound indeionized water. The cloud point corresponds to the temperature at whichthe solution has a transmittance equal to 85% of light rays having awavelength between 400 and 800 nm.

In other words, the temperature at which the solution has 85%transmittance corresponds to the minimum LCST transition temperature ofthe compound, in this case, from the LCST macromonomer.

In general, a transparent composition has a maximum light transmittancevalue, regardless of the wavelength between 400 and 800 nm, through a1-cm-thick sample, of at least 85%, preferably at least 90%. This is thereason why the cloud point corresponds to a transmittance of 85%.

In general, the LCST macromonomer is obtained by synthesis of an LCSToligomer having a functional end, then by grafting an ethylenic grouponto this functional end.

Mention may thus be made, by way of example, of the synthesis of theLCST macromonomer from an LCST oligomer of controlled size andfunctionality, carried out using a radical or ionic initiator having thedesired chemical function, and/or by introducing a transfer agentsubstituted by the desired chemical group and/or by polycondensation.

The LCST monomers which may be used to produce the LCST oligomer, whichis used to obtain the LCST macromonomer, are preferably selected fromN-isopropylacrylamide; N,N-dimethylacrylamide; acryloyl morpholine;N,N-diethyl acrylamide; N-tert-butyl acrylamide; N-vinyl caprolactam;and diacetone acrylamide.

In the context of the invention, the LCST oligomer advantageouslycomprises between 10 mol % and 100 mol % of monomer(s) comprising anLCST unit, more advantageously between 40 mol % and 100 mol % and evenmore advantageously between 50 mol % and 100 mol % relative to the totalnumber of moles of monomers in the oligomer. According to a particularembodiment, the LCST oligomer may, in particular, comprise 90 to 96 mol% of monomer(s) comprising an LCST unit.

In addition to the LCST monomers, the water-soluble monomers which maybe used to make the LCST oligomer are preferably selected from nonionicmonomers, anionic monomers, cationic monomers and zwitterionic monomers.Preferably, they are selected from nonionic monomers and anionicmonomers.

In the context of the invention, the LCST oligomer advantageouslycomprises between 0 mol % and 90 mol % of this (these) (nonionic and/oranionic and/or cationic and/or zwitterionic) monomer(s), moreadvantageously between 0 mol % and 60 mol % and even more advantageouslybetween 0 mol % and 50 mol % relative to the total number of moles ofmonomers in the oligomer. According to a particular embodiment, the LCSToligomer may, in particular, comprise 4 to 10 mol % of this (these)monomer(s). These monomers may be hydrophilic or hydrophobic in nature.

Thus, the LCST oligomer, and therefore the LCST macromonomer, isobtained from at least one LCST monomer and, optionally, at least onewater-soluble monomer. Therefore, it contains monomer units derived fromthe monomer(s) and macromonomer(s) mentioned.

The water-soluble monomer may be a nonionic monomer which may, inparticular, be selected from the group comprising vinyl monomers solublein water, and particularly acrylamide. Thus, the LCST oligomer maycomprise a nonionic monomer advantageously selected from the groupcomprising acrylamide; methacrylamide; N-vinylformamide; andN-vinylpyrrolidone.

The water-soluble monomer of the LCST oligomer may also be an anionicmonomer. The anionic monomer(s) of the LCST oligomer may be selectedfrom a broad group. These monomers may have at least one function fromvinyl functions (such as, acrylic, maleic, fumaric, itaconic, allylic)or a malonic function, and may contain at least one group from thecarboxylate, phosphonate, phosphate, sulphate, sulphonate groups, oranother anionically charged group. The anionic monomer of the LCSToligomer may be in acid form or in the form of an alkaline earth metalor an alkali metal or ammonium salt (in particular, quaternary).Examples of suitable monomers include acrylic acid; methacrylic acid;itaconic acid; crotonic acid; maleic acid; fumaric acid; monomers ofstrong acid type exhibiting, for example, a function of sulfonic acid orphosphonic acid type, such as 2-acrylamido 2-methylpropanesulfonic acid,vinylsulfonic acid, vinylphosphonic acid, allylsulfonic acid,allylphosphonic acid, styrene sulfonic acid; and the water-soluble saltsof these monomers such as their alkali metal, alkaline earth metal orammonium (in particular quaternary) salts.

Optionally, the LCST oligomer may include at least one cationic monomer.

The monomer of the LCST oligomer may optionally be a cationic monomer ofvinyl type (for example, acrylamide, acrylic, allylic or maleic) havinga quaternary ammonium function. Mention may be made, in particular andwithout limitation, of quaternized or salified dimethylaminoethylacrylate (ADAME); quaternized or salified dimethylaminoethylmethacrylate (MADAME); dimethyldiallylammonium chloride (DADMAC);acrylamido propyltrimethyl ammonium chloride (APTAC); and methacrylamidopropyltrimethyl ammonium chloride (MAPTAC).

Hydrophobic monomers may also be used to prepare the LCST oligomer. Theymay be selected, in particular, from vinyl type monomers (for exampleacrylamide, acrylic, allylic or maleic) having a pendant hydrophobicfunction. It may, in particular, be the butyl methacrylate monomer.

According to a preferred embodiment, the LCST oligomer is a polymer ofan LCST monomer (preferably N-isopropylacrylamide), of an anionicmonomer (preferably acrylic acid) and of a hydrophobic monomer(preferably butyl methacrylate).

Thus, according to another preferred embodiment, the LCST oligomer is apolymer of an LCST monomer (preferably N-isopropylacrylamide), of acationic monomer (preferably MADAME.MeCl) and of a hydrophobic monomer(preferably butyl methacrylate).

As regards the synthesis of the LCST macromonomer, in a first step,mention may be made of telomerization, which is a method of synthesizingan LSCT oligomer with low molar masses (called telomers).

According to the invention, the LCST macromonomer has a molecular weightpreferably between 500 g/mol and 200,000 g/mol, more preferably between1,000 g/mol and 100,000 g/mol, even more preferably between 1,500 g/moland 100,000 g/mol. Molecular weight is referred to as weight averagemolecular weight.

The telogen agents may be selected, inter alia, from thiols, alcohols,disulfides, phosphorus derivatives, boron derivatives and halogenderivatives. They may, in particular, make it possible to introducespecific functions at the end of the telomer chains, for example silane,trialkoxysilane, amine, epoxy, hydroxyl, phosphonate or acid functions.

Once these LCST oligomers have been formed, in a second step, a vinyldouble bond (R1R2C═CR3-, R1, R2 and R3 being, independently of oneanother, a hydrogen atom or a hydrocarbon or a non-hydrocarbon group,which may comprise heteroatoms) may be introduced at the end of thechain so that they serve as LCST macromonomers which, in turn, may bepolymerized.

According to another synthesis method, an LCST macromonomer may beobtained by controlled radical polymerization known as RAFT(Reversible-Addition Fragmentation chain Transfer) of LCST monomers inthe presence of at least one crosslinking agent. Therefore, themacromonomer thus obtained is structured and may be used as a core forobtaining water-soluble copolymers in star-shaped form. The crosslinkingagent may, in particular, be selected from the group comprisingpolyethylene unsaturated monomers (having at least two C═C unsaturatedfunctions), such as, for example, vinyl, allylic and acrylic functionsand, for example, and mention may be made, for example, of methylene bisacrylamide (MBA).

The LCST macromonomer may be obtained by the same technique but withoutusing a crosslinking agent.

There are numerous reactions that may be implemented for couplings onmonomers: alkylation, esterification, amidation, transesterification ortransamidation.

In a preferred embodiment, the preparation of the LCST macromonomer iscarried out by radical reaction between an LCST oligomer and a compoundcontaining a C═C double bond, the double bond still being present aftersaid radical reaction. Advantageously, the LCST oligomer has thecharacteristic of having a nitrogen or oxygen atom at its end, such as,for example, an alcohol or amine function, which is functionalized usinga compound containing a C═C double bond. This compound containing adouble bond is preferably selected from acryloyl chloride, acrylic acid,methacryloyl chloride, methacrylic acid, maleic anhydride, methacrylicanhydride, unsaturated aliphatic isocyanates, allyl chloride, allylbromide, glycidyl acrylate, glycidyl methacrylate.

According to a particular embodiment, the LCST macromonomer may be offormula (I):

In which:

m is an integer advantageously between 2 and 40.

The LCST groups of the water-soluble polymer have a transitiontemperature by heating advantageously between 0 and 180° C. for a massconcentration in deionized water of 1% by weight of said LCST groups,preferably between 0 and 100° C., even more preferably between 10 and80° C.

Inverse Polymer Emulsion

An inverse emulsion, otherwise called a water-in-oil emulsion, iscomposed of an oily phase, generally a lipophilic solvent or an oil,which constitutes the continuous phase in which water dropletscomprising a polymer are in suspension, these water droplets forming adispersed phase. An emulsifying surfactant (called water-in-oilsurfactant) at the water/oil interface stabilizes the dispersed phase(water+polymer) in the continuous phase (lipophilic solvent or oil).

In inverse emulsions according to the prior art, an oil-in-watersurfactant, which is an inverting agent, makes it possible to invert theemulsion and therefore to release the polymer when the emulsion is mixedwith an aqueous fluid. For the purposes of the invention, it is notnecessary to add an inverting surfactant (oil-in-water surfactant) tothe inverse emulsion, including during its use. In other words, andpreferably, the inverse emulsion according to the invention does notcontain an oil-in-water surfactant and, in general, it is not necessaryto add an oil-in-water surfactant in the fluid in which the emulsion isimplemented, whether before, during or after the addition of the inverseemulsion in said fluid.

The inverse emulsion according to the invention may be preparedaccording to any method known to a person skilled in the art. Generally,an aqueous solution comprising the monomer(s) and the water-in-oilsurfactant(s) is emulsified in an oily phase. Then, the polymerizationof the monomers is carried out, advantageously by adding a free radicalinitiator.

Generally, the polymerization is carried out isothermally, adiabaticallyor at controlled temperature. In other words, the temperature is keptconstant, usually between 10 and 60° C. (isothermal), or the temperatureincreases naturally (adiabatic) and, in this case, the reaction usuallystarts at a temperature below 10° C. and the final temperature isgenerally above 50° C. or, finally, the increase in temperature iscontrolled so as to have a temperature curve between the isothermalcurve and the adiabatic curve.

The inverse emulsion according to the invention is preferably preparedaccording to the process comprising the following steps:

-   a) preparing an aqueous phase comprising at least one water-soluble    monomer and at least one LCST macromonomer,-   b) preparing an oily phase comprising at least one oil and at least    one water-in-oil surfactant,-   c) mixing the aqueous phase and the oily phase in order to form an    inverse emulsion,-   d) once the inverse emulsion is formed, polymerizing the monomers in    the aqueous phase using a radical polymerization initiator.

In the inverse emulsion, the weight ratio of the aqueous phase to theoily phase is preferably from 30:70 to 90:10, more preferably from 70:30to 80:20.

At the end of the polymerization reaction, it is also possible to diluteor concentrate the inverse emulsion obtained. Dilution is usually doneby adding water, preferably salted, in the inverse emulsion. In thiscase, the inverse emulsion may be diluted to obtain a polymerconcentration of up to 10% by weight. It is possible to concentrate theemulsion obtained, for example by distillation. In this case, theinverse emulsion may be concentrated and a polymer concentration of upto 60% by weight may be obtained.

As already discussed above, it is not necessary to add an invertingsurfactant (oil-in-water surfactant) to the inverse emulsion during itspreparation. In addition, the use of the inverse emulsion does notrequire an inverting surfactant.

However, it is possible to introduce an inverting surfactant. Indeed, asmentioned above, the object of the invention is to limit, and eveneliminate, the use of an inverting surfactant to invert an inverseemulsion.

The oil of the inverse emulsion according to the inventionadvantageously denotes an oil or a solvent immiscible in water. The oilused to prepare the water-in-oil emulsion of the invention may bemineral oil, vegetable oil, synthetic oil, or a mixture of several ofthese oils. Examples of mineral oil are mineral oils containingsaturated hydrocarbons of the aliphatic, naphthenic, paraffinic,isoparaffinic, cycloparaffinic or naphthyl type. Examples of syntheticoil are hydrogenated polydecene or hydrogenated polyisobutene; an estersuch as octyl stearate or butyl oleate. ExxonMobil's Exxsol® productsare suitable oils.

The inverse emulsion preferably comprises from 12 to 50% by weight ofoil or lipophilic solvent, more preferably from 15 to 30% by weight.

The water-in-oil emulsion of step a) above preferably comprises from 30to 55% by weight of water, more preferably from 35 to 48% by weight.

In the present invention, the term “inverse emulsion surfactant” or“emulsifying agent” or “water-in-oil surfactant” refers to an agentcapable of emulsifying water in oil while an “inverting agent” or“oil-in-water surfactant” refers to an agent capable of emulsifying oilin water. More specifically, it is considered that an inverting agent isa surfactant having an HLB greater than or equal to 10, and that anemulsifying agent is a surfactant having an HLB less than 10.

The hydrophilic-lipophilic balance (HLB) of a chemical compound is ameasure of the degree of hydrophilicity or lipophilicity, determined bycalculating values for different regions of the molecule, as describedby Griffin in 1949 (Griffin W C, Classification of Surface-Active Agentsby HLB, Journal of the Society of Cosmetic Chemists, 1949, 1, pages311-326).

In the present invention, we have adopted Griffin's method based oncalculating a value based on the chemical groups of the molecule.Griffin assigned a dimensionless number between 0 and 20 to provideinformation on water and oil solubility. Substances with an HLB value of10 are distributed between the two phases so that the hydrophilic group(molecular mass Mh) projects completely into the water while thelipophilic group (usually a hydrophobic hydrocarbon group) (molecularmass Mp) is in the non-aqueous phase.

The HLB value of a substance having a total molecular mass M, ahydrophilic part of a molecular mass Mh and a lipophilic part of amolecular mass Mp is given by the following formula:HLB=20(Mh/M)

The emulsifying agent (water-in-oil surfactant) may, in particular, beselected from surfactant polymers such as:

-   -   polyesters having a weight average molecular weight of between        1000 and 3000 g/mol, for example the products of condensation        between a polyisobutenyl succinic acid or its anhydride and a        polyethylene glycol,    -   block polymers having an average molecular weight by weight        advantageously between 2500 and 3500 g/mol, for example those        sold under the names Hypermer®,    -   sorbitan extracts such as sorbitan monooleate, sorbitan        isostearate or sorbitan sesquioleate,    -   sorbitan esters,    -   diethoxylated oleoketyl alcohol    -   tetraethoxylated lauryl acrylate,    -   condensation products of higher fatty alcohols with ethylene        oxide, such as the reaction product of oleyl alcohol with 2        ethylene oxide units;    -   condensation products of alkylphenols and ethylene oxide, such        as the reaction product of nonylphenol with 4 units of ethylene        oxide.

Products such as Witcamide® 511, betaine-based products and ethoxylatedamines may also be used as water-in-oil emulsifiers.

The inverse emulsion may contain several water-in-oil emulsifyingagents. It preferably contains between 0.8 and 20% by weight ofwater-in-oil emulsifier, more preferably between 1 and 10% by weight.

The radical polymerization initiator may be selected from initiatorsconventionally used in radical polymerization. These may be, forexample, hydrogen peroxides, azo compounds or redox systems.

The water-in-oil emulsion according to the invention preferablycomprises from 8 to 60% by weight of polymer, preferably from 12 to 40%.

The inverse emulsion may comprise from 1 to 40% by weight of salts,preferably from 3 to 30% by weight, more preferably from 5 to 25% byweight of salts.

The salts present in the water-in-oil emulsion may be, for example,sodium salts, lithium salts, potassium salts, magnesium salts, aluminumsalts, ammonium salts, phosphate salts, sulfate salts, chloride salts,fluoride salts, citrate salts, acetate salts, tartrate salts, hydrogenphosphate salts, water-soluble inorganic salts, other inorganic saltsand their mixtures. These salts include sodium chloride, sodium sulfate,sodium bromide, ammonium chloride, lithium chloride, potassium chloride,potassium bromide, magnesium sulfate, aluminum sulfate, and theirmixtures. Sodium chloride, ammonium chloride and ammonium sulfate arepreferred and their mixtures are even more preferred.

Property of the Inverse Emulsion

Thanks to the presence of LCST macromonomer units in the polymer, theinverse emulsion is capable of auto-inverting when it is used in wateror a brine, although said emulsion may advantageously contain noinverting surfactant. In the absence of LCST macromonomer units in thepolymer, inversion of the inverse emulsion requires the presence of aninverting surfactant such as an oil-in-water surfactant.

Thus, this particular property makes it possible to solve theenvironmental problems linked to the presence of an invertingsurfactant. It also makes it possible to simplify the formulation ofsuch emulsions.

This last advantage is particularly interesting when the surfactantsmust be selected specifically according to the composition of the mediumin which the inverse emulsion is implemented (water or brine), andaccording to the temperature of that medium, which is the case in oiland gas recovery.

Uses of the Inverse Emulsion

The present invention also relates to a polymeric aqueous solutionobtained by inversion of the inverse emulsion as described above in anaqueous medium, preferably in the absence of an oil-in-water surfactant.In other words, it is a process for inverting an inverse emulsionconsisting in bringing it into contact with an aqueous medium,preferably in the absence of an oil-in-water surfactant.

The present invention also relates to the use of the inverse emulsion tothicken an aqueous medium, to flocculate suspended particles or toreduce the level of frictional resistance during transport of an aqueousmedium.

Finally, the present invention also relates to the use of the inverseemulsion in the oil and gas recovery, in water treatment, in slurrytreatment, in paper manufacturing, in construction, in the miningindustry, in the formulation of cosmetic products, in the formulation ofdetergents, in textile manufacturing, or in agriculture.

Usually, the inverse emulsion is implemented by adding most often water,or a brine (such as sea water), in an aqueous medium. The polymer isreleased and dissolved or swelled in the aqueous medium.

The inverse emulsion may be advantageously prepared with the device andmethod of U.S. Pat. No. 8,383,560, in which the inverse emulsion isdissolved continuously with an arrangement of multiple static mixers.

The inverse emulsion is used such that the polymer concentration in themedium in which it is implemented is advantageously between 25 and100,000 ppm by weight, more preferably between 50 and 10,000 ppm. Thisamount of polymer depends on the process in which the inverse emulsionis used.

The inverse emulsion according to the invention is particularly usefulin the recovery of oil and gas. Indeed, oil and gas recovery companiesuse large quantities of inverse polymer emulsion and seek to limit theenvironmental impacts of their activities.

In addition, the inverse emulsions according to the invention canauto-invert under many conditions. More precisely, they auto-invert evenunder conditions generally considered difficult, or even extreme, inparticular when the aqueous medium in which they are used is very saltyand/or when their temperature is high. These advantages are highlysought after in the field of oil and gas recovery.

The inverse emulsion according to the invention is capable ofauto-inverting in sea water but also in very concentrated brines.

Likewise, the inverse emulsion according to the invention is capable ofauto-inverting even at high temperatures.

Oil and gas recovery processes are generally treatments of subterraneanformations in which a polymer is used to increase the viscosity of theaqueous injection fluid and/or to reduce the level of frictionalresistance that occurs during the injection of said fluid into asubterranean formation, or even to punctually or permanently plug a partof the subterranean formation.

These subterranean treatments include, but are not limited to, drillingoperations, stimulation treatments such as fracturing operations,completion operations and the improved process of oil recovery bysweeping with a polymer solution.

The present invention also relates to a method for fracturing anunderground formation, which comprises:

-   aa) providing an inverse emulsion as described above;-   bb) inverting the inverse emulsion by adding it to an aqueous fluid    in order to form an injection fluid;-   cc) optionally, adding at least one propping agent in the injection    fluid;-   dd) introducing the injection fluid into part of the subterranean    formation;-   ee) fracturing the underground formation with the injection fluid.

The present invention also relates to a process for the improvedrecovery of hydrocarbons (oil and/or gas) by sweeping in a subterraneanformation, which comprises:

-   aaa) providing an inverse emulsion as described above;-   bbb) inverting the inverse emulsion by adding it to an aqueous fluid    to form an injection fluid;-   ccc) introducing the injection fluid into part of the subterranean    formation;-   ddd) sweeping part of the subterranean formation with the injection    fluid;-   eee) recovering a mixture of hydrocarbons and aqueous fluid.

The following characteristics apply to the previous two processes(fracturing and oil and/or gas recovery).

Advantageously, the inverse emulsion according to the invention does notcontain an inverting surfactant and it is advantageously not necessaryto add an inverting surfactant in the fluid in which the inverseemulsion is implemented, whether before, during or after adding theinverse emulsion to said fluid. Thus, advantageously, the use of theinverse emulsion according to the invention does not require thepresence of an oil-in-water surfactant.

The aqueous fluid may be a brine containing monovalent and/or polyvalentsalts or combinations thereof. Examples of salts include, withoutlimitation, sodium salts, lithium salts, potassium salts, magnesiumsalts, aluminum salts, ammonium salts, phosphate salts, sulfate salts,chloride salts, fluorinated salts, citrate salts, acetate salts,tartrate salts, hydrogen phosphate salts, soluble inorganic salts, otherinorganic salts and mixtures thereof.

The brine may contain more than 30,000 ppm of salts, preferably morethan 70,000 ppm, even more preferably more than 100,000 ppm. The brinemay be saturated with salts.

The temperature of the aqueous fluid in which the inverse emulsionaccording to the invention is inverted is advantageously between 25° C.and 160° C., preferably greater than 40° C., more preferably greaterthan 60° C., even more preferably greater than 80° C., and even morepreferably greater than 90° C.

The concentration of water-soluble copolymer in the aqueous injectionfluid is advantageously between 50 and 50,000 ppm by weight, preferablybetween 100 and 30,000 ppm, more preferably between 500 and 10,000 ppmrelative to the weight of the injection fluid.

The injection fluid may also include other components such as analkaline agent, a propping agent, corrosion inhibitors, acids, scaleinhibitors, guars, guar derivatives, crosslinkers such as zirconium,titanate or borate.

The water or brine used for the preparation of the injection fluid maybe produced water. The term “produced water” refers to all salted orunsalted water, brines, sea water, aquifer water which come from ahydrocarbon reservoir. This produced water may be treated prior to thepreparation of the injection fluid, for example as described in patentapplication WO 2018/020175.

Advantageously, the injection fluid has, at the time of its injection, aviscosity of between 1 and 200 cps (centipoise) (viscosity measurementsat 20° C. with a Brookfield viscometer equipped with a UL module and ata speed of 6 rpm).

The implementation of the inverse emulsion according to the invention iscarried out on site, just upstream of the injection, into the oil field,of the injection fluid in which it is implemented. In general, theinverse emulsion is added to a more or less salty brine depending on theoil fields. Other components, such as, for example, biocides,anti-corrosion agents, or propping agents, are also introduced into thisfluid to prepare the injection fluid. Most often, they are added to acirculation line of the aqueous solution or the brine.

The present invention will be disclosed in more detail with reference tothe following examples and figures. The following examples simplyillustrate the invention and are not intended to be limiting. Unlessotherwise indicated, all percentages are by weight.

FIGURES

FIG. 1 is a graph showing the change in the percentage of inversion ofthe EM1 inverse emulsion over time, in different fluids at a temperatureof 25° C.

FIG. 2 is a graph showing the change in the percentage of inversion ofthe EM1 inverse emulsion over time, in different fluids at a temperatureof 80° C.

FIG. 3 is a graph showing the change in the percentage of inversion ofthe EM2 inverse emulsion over time, in different fluids at a temperatureof 25° C.

FIG. 4 is a graph showing the change in the percentage of inversion ofthe EM2 inverse emulsion over time, in different fluids at a temperatureof 80° C.

EXAMPLES OF EMBODIMENT OF THE INVENTION

1/ Synthesis of Telomers (or LCST Oligomers)

To prepare a Telomere called T1, the following process is carried out.

In a dual jacketed reactor:

A hydroalcoholic solution (410 g) and the N-isopropylacrylamide (NIPAM,113 g, or 1 mol), butyl methacrylate (7.9 g, or 0.055 mol) and acrylicacid (4.44 g, or 0.055 mol) monomers are loaded.

-   -   The mixture is stirred.    -   The pH of the mixture is adjusted to between 4.0 and 5.0 using a        40% by weight NaOH solution in water.    -   The mixture obtained is heated to 50° C.    -   The mixture is de-oxygenated with nitrogen bubbling for 40        minutes.    -   Aminoethanethiol HCl (2.5 g) is added.    -   2,2′-azobis(2-methylpropionamidine)dihydrochloride (0.22 g) is        added to initiate telomerization.    -   After stabilization of the temperature, the mixture is stirred        for 2 hours and then cooled to 25° C.

A concentrated viscous solution containing 23% by weight of a telomerwith a degree of polymerization of 50 monomer units (DPn 50) isobtained. The LCST of this T1 telomere was estimated at 38° C. accordingto the process described above.

To prepare a Telomere called T2, the following process is carried out.

In a dual jacketed reactor:

-   -   The N-isopropylacrylamide (NIPAM, 113 g, or 1 mol), butyl        methacrylate (4.44 g, or 0.031 mol) and chloromethyl        dimethylamino-ethyl methacrylate (MADAME.MeCl, 2.16 g, or 0.01        mol) monomers are loaded in 445 g of a hydroalcoholic solution.    -   The mixture is stirred.    -   The pH of the mixture is adjusted to between 4.0 and 5.0 using a        40% by weight NaOH solution in water.    -   The mixture obtained is heated to 50° C.    -   The mixture is de-oxygenated with nitrogen bubbling for 40        minutes.    -   Aminoethanethiol HCl (2.35 g) is added.    -   2,2′-azobis(2-methylpropionamidine)dihydrochloride (0.22 g) is        added to initiate the polymerization.    -   After stabilization of the temperature, the mixture is stirred        for 2 hours and then cooled to 25° C.

A concentrated viscous solution containing 21% by weight of a telomerwith a degree of polymerization of 50 monomer units (DPn 50) isobtained. The LCST of this T2 telomere was estimated at 32° C. accordingto the process described above.

TABLE 1 List and monomeric compositions of T1 and T2 telomeres. LCSTHydrophilic Hydrophobic LCST monomer monomer (B), monomer (C), telomereTelomere (A), mol % mol % mol % (° C.) T1 NIPAM, 90 Acrylic acid, Butyl38 5 methacrylate, 5 T2 NIPAM 96 MADAME•MeCl, Butyl 32 1 methacrylate, 32/ Synthesis of Macromonomers

The following process is carried out to prepare a macromonomer calledM1.

In a dual jacketed reactor:

-   -   400 g of Telomere T1 solution (5581 g/mol) at 23% by weight are        loaded in water.    -   The solution is stirred.    -   The pH of the solution is adjusted to 7.5 using a 40% by weight        NaOH solution in water.    -   The solution is cooled to 5° C.    -   Using a burette, 3.0 g of acryloyl chloride are added dropwise.    -   The pH is continuously adjusted between 7 and 9 using a 40% by        weight NaOH solution in water.    -   The temperature is maintained at 5° C. throughout the reaction.    -   After the end of the reaction, the solution is stirred for 2        hours while continuously checking the pH.

A concentrated viscous solution containing 21.5% by weight of LCSTmacromonomer M1 (5711 g/mol) is obtained.

The macromonomer M2 is prepared using the same process, with the telomerT2 (5740 g/mol). A concentrated viscous solution containing 21.5% byweight of LCST macromonomer M2 (5869 g/mol) is obtained.

3/ Synthesis of Polymers in Inverse Emulsion

The following process is carried out to prepare an inverse emulsioncalled EM1.

In order to prepare the aqueous solution of monomers, 146 g (74.997 mol%) of acrylamide, 157 g (25 mol %) of ATBS (2-acrylamido 2-methylpropanesulfonic acid), 0.5 g (0.003 mol %) of LCST macromonomer M1 and 370 g ofwater are loaded into a beaker. The pH of the monomer solution isadjusted between 5 and 6 using NaOH.

The following additives are added:

-   -   0.37 g of Versenex 80 (complexing agent),    -   1.29 g of TBHP (terbutylhydroperoxide) (oxidant).

295 g of Exxsol D100 and 30 g of Span 80 are mixed before beingtransferred into a reactor together with the aqueous phase.Emulsification of the two-phase mixture is carried out using a mixer,this mixture is deoxygenated using an inert gas and then cooled to atemperature of 15° C.

The synthesis starts with the addition of a solution of MBS (sodiummetabisulphite, 1 g/l) at a flow rate of 1 ml/min. The temperature ofthe medium increases until it reaches a value of 40° C., which ismaintained for 2 hours.

The reaction medium is allowed to cool. An inverse emulsion with apolymer concentration of 30% by weight is thus obtained.

An EM2 inverse emulsion is prepared according to the same process, withthe LCST macromonomer M2. An EM2 inverse emulsion with a polymerconcentration of 30% by weight is obtained.

As a counterexample, the EM3 inverse emulsion is prepared according tothe same process, but without using an LCST macromonomer. In otherwords, the 0.003 mol % of LCST macromonomer is replaced by 0.003 mol %of acrylamide.

4/ Test

The test consists of studying the inversion of inverse emulsions overtime, in different brines and at different temperatures. The inversionis characterized by a release of the polymer chains into the aqueousmedium and thus by an increase in its viscosity.

Materials and Method

The speed of inversion is studied using Thermo instrument's iQRheometer. During the inversion test, the stress is recorded as afunction of time. It increases in proportion to the viscosity released.

The EM1, EM2 and EM3 inverse emulsions are tested, without any invertingagent being added to them.

Four different fluids were used: tap water, and three brines ofdifferent concentrations: 15,000 TDS (Total Dissolved Solids) (1.5% byweight of NaCl), 33,000 TDS (3% by weight of NaCl and 0.3% by weight ofCaCl₂)), and 100,000 TDS (10% by weight of NaCl). The TDS corresponds tothe quantity in ppm of organic and inorganic substances contained in abrine. In other words, 15,000 TDS equals 15,000 mg of salt per liter offluid.

The tests were carried out at 2 different temperatures: 25° C. and 80°C.

To this end, 1.2 g of inverse emulsion are injected into 34 ml of brineunder rotation of the elliptical module (U1) at 800 rpm. The emulsionsare tested such that the polymer concentration is 10,000 ppm (by weight)in the four fluids. Another test is carried out with the same emulsionsbut at a concentration of 100 ppm (by weight), only in brine (33,000TDS).

5/ Results

The test results are recorded in the graphs of FIGS. 1 to 4 . In thesefigures, the curves for the EM3 inverse emulsion are identical,regardless of the nature of the fluid and the temperature. Therefore,only one curve appears for the EM3 emulsion, that implemented in a brineof 33,000 TDS.

As shown in FIGS. 1 and 2 , the EM1 inverse emulsion according to theinvention, in which the polymers comprise M1 macromonomer units, rapidlyinverts in a very wide range of brine compositions ranging from tapwater to a 10% salt brine (100,000 TDS), both at low temperature (25°C.) and at high temperature (80° C.). The EM1 emulsion also inverts verywell at 100 ppm in brine at 33,000 TDS.

Conversely, the EM3 inverse emulsion, which does not include an LCSTmacromonomeric unit, does not invert at all regardless of the fluid andthe temperature.

The same results are obtained with the EM2 inverse emulsion as shown inFIGS. 3 and 4. The EM2 emulsion inverts under all brine and temperatureconditions, while the EM3 emulsion does not invert. The EM2 emulsionalso inverts very well at 100 ppm in brine at 33,000 TDS.

Consequently, the auto-inverting behavior of the EM1 and EM2 emulsionsaccording to the invention is clearly observed, while these emulsions donot contain an inverting agent.

These auto-inverting properties are highly sought after by users ofinverse emulsions because they avoid all of the potential problemsassociated with the use of an inverting agent.

The invention claimed is:
 1. An auto-invertible inverse emulsioncomprising: oil; water; at least one water-in-oil surfactant; and atleast one polymer having a molecular weight of between 5 and 30 milliong/mol and containing monomer units of at least acrylamide, 2-acrylamido2-methylpropane sulfonic acid (ATBS), and 10⁻⁵ to 5 mol % of a lowercritical solution temperature (LCST) macromonomer, said LCSTmacromonomer having a molecular weight of between 500 and 200,000 g/moland having units from: at least one anionic monomer selected fromacrylic acid and ATBS; and at least one LCST monomer selected fromdiethylacrylamide, N-isopropylacrylamide, dimethylacrylamide, andter-butylacrylamide.
 2. The inverse emulsion according to claim 1,wherein the inverse emulsion is free of oil-in-water surfactant.
 3. Amethod for preparing an inverse emulsion according to claim 1, saidmethod comprising the following steps: a) preparing an aqueous phasecomprising at least one water-soluble monomer and at least one LCSTmacromonomer, b) preparing an oily phase comprising at least one oil andat least one water-in-oil surfactant, c) mixing the aqueous phase andthe oily phase in order to form an inverse emulsion, and d) once theinverse emulsion is formed, polymerizing the monomers in the aqueousphase using a radical polymerization initiator.
 4. A polymeric aqueoussolution obtained by inversion of the inverse emulsion according toclaim 1 in an aqueous medium in the absence of an oil-in-watersurfactant.
 5. Use of the inverse emulsion according to claim 1 forthickening an aqueous medium, for flocculating suspended particles orfor reducing the level of frictional resistance during transport of anaqueous medium.
 6. A method for fracturing an underground formation,which comprises: aa) providing an inverse emulsion according to claim 1;bb) inverting the inverse emulsion by adding it to an aqueous fluid inorder to form an injection fluid; cc) optionally, adding at least onepropping agent in the injection fluid; dd) introducing the injectionfluid into part of the subterranean formation; and ee) fracturing theunderground formation with the injection fluid.
 7. A method for theimproved recovery of hydrocarbons by sweeping in an undergroundformation, which comprises: aaa) providing an inverse emulsion accordingto claim 1; bbb) inverting the inverse emulsion by adding it to anaqueous fluid in order to form an injection fluid; ccc) introducing theinjection fluid into part of the subterranean formation; ddd) sweepingpart of the subterranean formation with the injection fluid; and eee)recovering a mixture of hydrocarbons, gas and aqueous fluid.
 8. Theinverse emulsion according to claim 1, wherein the LCST macromonomer hasa weight average molecular weight between 1,000 and 100,000 g/mol.